Temperature-compensating means for maintaining constant frequency in tuning forks



Dec. 27, 1927. 1,65%794- H. A. WHITEHORN TEMPERATURE COMPENSATING MEANS FOR MAINTAINING CONSTANT FREQUENCY m TUNING FORKS Filed Oct. 20. 1925 lnvenfor': Homer 14. Whilkham Patented Dec. 27, 1927.

UNITED STATES PATENT OFFICE.

HOMER A. WHITEHORN, OF NORWOOD, ILLINOIS, ASSIGNOR TO WESTERN ELECTRIC COMPANY, INCORPORATED, OF NEW YORK, N. Y., A CORPORATION OF NEW YORK.

TEMPERATURE-COMPENSATING MEANS FOR MAINTAINING CONSTANT FREQUENCY 1N TUNING FORKS.

Application filed October 20, 1925. Serial No. 63,701.

This invention relates to means for maintaining uniform periods of vibrationin vibrating devices which are subjected to changes in temperature.

In various telegraph systems, such as the well known multiplex systems, it is necessary for satisfactory operation to maintain the apparatus at the various stat-ions in very close synchronism. Approximate synchro- 1c nism is ordinarily obtained by driving the mechanism at the respective stations by means of an impulse motor of the LaCour type, the impulses for which are obtained from carefully adjusted tuning forks arranged to be electrically driven. As is well known in devices of this nature, changes in temperature cause changes in the length of the fork tine and also in the elasticity of its material thereby affecting the period of vibration and hence the synchronism of the various apparatus. Q

- The object of this invention is to overcome this change due to variations in tem perature, and to accomplish this the efiect produced when two metals, having diflerent coeficients of expansion are firmly joined to each other and subjected to the same temperature variation, is utilized.

This invention will be better understood from thefollowing description together with the attached drawings showing preferred forms of the invention and in which; 0

Fig. 1 shows a manner of applying the 1nvention to a tuning fork to make it selfcompensating.

Fig. 2 represents diagrammatically a ten ing fork used to control the speed of an 1111- pulse motor of the LaCour type; and

Fig. 3 shows a manner of applying the co invention to the support of a permanent magnet used to vary the period of vibration of the fork.

Referring now to Fig. 1 in which one tine of the fork is shown broken away, there is es welded or otherwise permanently fixed to tine 21 a piece of metal 22 having a larger coeficient of expansion than the metal from which the fork is made. The end of the tine is bent substantially as shown. The

other tine is arranged in the same manner.

Upon an increase in temperature, the elongation of the tine incident thereto would decrease the rate of vibration, and to a still greater degree would the change in elasticity decrease the rate. Since the piece 22 has a higher coeflicient of expansion, the bent portion will be inclined back toward the fixed or non-vibrating part of the fork. This bending back of aportion of the tine compensates for both of above mentioned effects so that the period of vibration remains substantially unchanged throughout a considerable range of temperature variations.

With a decrease in temperature, the tendency is to increase the rate of vibration, but here again the piece 22 will contract more than the tine proper and hence the turned up portion will be bent away from the fixed end of the fork, thereby compensating for the decrease in temperature.

. In Fig. 2 is shown a fork utilized for drivmg a synchronous motor at constant speed. Here the fork 1 has pieces of metal 12 and 13 fixed'to the tines 5 and 6 substantially as shown in Fig. 1, the metal from which the pieces 12 and 13 are made having a larger coefficient of expansion.

The fork is caused to vibrate by electromagnet 3 from a source of current 2 in the well known manner. A pair of contacts 7 and 8 are on opposite sides of tine 6 and are alternately engaged thereby which serves to impress current impulses from source 2 alternately on magnets 9-9 and 10-10 of a LaCour motor of the well known type. A permanent magnet 11 is placed near the end of the tines substantially as shown and tends to keep the vibrations of the fork constant in the following manner: I

As explained above, in connection with Fig. 1, an increase in temperature tends to decrease the speed of vibration. However, since the pieces of metal 12 and 13 have a larger coeficient of expansion than the tines,

1 the ends of the tines are curved upward decreasing the air-gap between them and the pole faces of the magnet 11. The decreased air-gap increases the field strength and this has the same efiect as stifiening the tines. The stifiening of the tines compensates for their elongation and reduced elasticity thereby causing the period of vibration to remain unchanged. With a decrease of temperature, the tines shorten and become more elastic and the air-gap is increased. The first two of these effects tend to increase the rate of vibration but the increased air-gap till permits more freedom to vibrate and hence the tendency to ahigher rate of vibration is counteracted.

In Fig. 3 is shown a modification wherein a permanent magnet 23 is mounted on the same base as the fork 24 in the general man ner shown. The support for the permanent magnet is made up of two metals having different coeflicients of expansion. A bolt 25 passing through the slot in piece 26 permits adjustment of the air-gap between the magnet and the fork to change the period of vibration. The outside piece 27 of the magnet support has the larger coefiicient of expansion and hence the effect of an increase in temperature is compensated, for by the decrease in the air-gap caused by the greater expansion of piece 27 which moves the magnet toward the fork. Also, a decrease in temperature shortening the tines increases the air-gap between the magnet and the fork due to the greater contraction of the piece 27. The period of vibration in each case .will remain unchanged.

It is understood that changes may be made in the above apparatus without departing from the spirit and scope of this invention which is to be limited only by the appended claims.

What is claimed is:

1. In combination, a vibratory member subject to temperature variations and thermally actuated means for changing the shape of said member and thereby compensating for the effect of temperature changes on the rate of vibration of said member.

2. In a vibrating device, a vibrating member, automatic means vibrating with said member and adapted to change the shape of said member to maintain the frequency of vibration of said vibrating member constant under temperature variations.

3. In a vibrating device, a vibrating member, a section of said vibrating member having a coefficient of expansion different from that of the main portion of said member, the relation of said section to the main portion being such that the frequency of vibrations of said vibrating member remains constant under changes in the shape of the section and the portion due to temperature variations thereof.

4. In combination with a metallic vibrating device, a magnetic member adjacent the free end of said vibrating device, automatic ated by variations in temperature to vary the distance between the end of said vibrating device and said magnetic member to maintain the frequency of vibration of said vibrating device constant.

6. In combination with a metallic vibrating device, a magnetic member adjacent the free end of the same, automatic means comprising two pieces of metal having different 7 coefficients of expansion, said pieces of metal being arranged to vary the distance between said vibrating device and said magnetic member with variations in temperature to thereby maintain .the frequency of said vibrating device constant.

7. In combination with a tuning fork, a permanent magnet controlling the frequency of vibration of said fork, the pole faces of said permanent magnet situated adjacent the free ends of the tines of said fork, automatic means comprising two pieces of metal having different coefficients of expansion arranged to vary the distance between said magnetic pole faces and said fork tines to thereby maintain the frequency of vibration of said fork constant. I

In witness whereof, I hereunto subscribe my name this 19th day of October A. D.',

HOMER A. WHITEHORN. 

